freediving after SCUBA

[phishphood]

Did a quick search but couldn't find anything directly related to the topic. But I'm hitting an overnight liveaboard with something like 5 dives over 2 days in AUS. We also get unlimited snorkeling. Snorkeling to me, being an abalone diver, means hitting 30' and looking around for a minute or so. Should I not be doing this? I have no clue what the dives will be like yet except it's on the GBR out of Cairns. At least 1 if not 2 of the people in our party will be snorkel-only and I'd like to keep them company if they want to go when we're not on a dive, but I don't know how well I can stop myself from freediving.

 

[DandyDon]

I'd call it dangerous, but I am not really qualified to explain why in detail. I hope someone will soon for you, but I am pretty sure that you'd be increasing chances of bends.

 

[Cave Diver]

This article should explain why it's a bad idea doing free diving after diving:

http://www.gue.com/?q=en/node/596

 

[smellzlikefish]

Many of us here have snorkeled after diving and are still around to talk about it. Because you are ascending repeatedly really fast while still loaded with nitrogen, I believe the issue is that the sudden changes in pressure will jar your system in such a way that encourages bubble formation. DAN just had an article on it in Alert Diver and I hope I didn't just botch the explanation. Whatever the reason, DAN recommends not doing it, but like any things SCUBA, there is some wiggle room where you'll probably be okay. Is 30 feet (~1 atm) deep enough to cause problems? The answer to that is an ugly shade of gray.

 

[fdog]

I've read enough accounts of freedivers being bent by freediving after scuba diving, that I won't do it - especially after a couple days of vacation diving, with a couple dives per day. There was a study done in Europe about 5 years ago or so that supports it, if you troll around in deeperblue.net you can find it.

The mechanism is bubble pumping. The ratio of pressure change from 30' is about 2:1, so you are actually in rather dangerous territory in that regard - bubbles will be shrunk to half their size. It's worth pointing out that unlike recreational scuba diving, where most DCS incidents are pain-only Type I hits, freediving-after-scuba-diving DCS is usually the more severe Type II involving CNS defects.

Simple surface snorkeling? Sure, that's perfectly okay; but I know myself well enough to know I just couldn't resist a nice simple 10 to 15 meter freedive, so I just don't do it.


All the best, James

 

[phishphood]

Thank you everyone for the info. I figured as much, but couldn't quite get it figured out in my head. I suppose I'll do my best to not go more than 5' under during my 'surface' intervals and hope for the best. On that note, would it be best just to treat freediving as flying and wait 24hr give or take after the last tank dive to completely off-gas?

James- I'm glad you understand my, er... pain at this decision and the self-restraint it calls for.

And for everyone: apologies I had to post this when there obviously have been multiple posts about it in the past. I can't find them when searching, but the forum "similar threads" tool pops up a ton of them

 

[DandyDon]

Ever shake a soda pop or beer, then open it? Not what you want to do with the dissolved Nitrogen in your blood. I wouldn't bounce to 5 ft. Paddling around is ok, but submerging pushes it.

Your dive computer has 2 after diving countdown clocks: 1 for the old 24 hour rule, and 1 for the more relevant time to clear. You should be okay after the latter one clears.

 

[knowone]

I didn't think they dived the Mariana trench out of Cairns?

 

[TRIG]

Not an answer to the question, but an interesting video clip;

Hunter goes deep sea fishing without air | VidAddict.com

 

[DandyDon]

Not an answer to the question, but an interesting video clip;

Hunter goes deep sea fishing without air | VidAddict.com

One of the sea gypsy tribe that has evolved thru survival. Diving like that would kill many of us from Shallow Water Blackout on ascent. They also pierce their eardrums I believe.